Retention Time and Depolarization in Organic Nonvolatile Memories Based on Ferroelectric Semiconductor Phase-Separated Blends

• Published in: IEEE transactions on electron devices 2010-12, Vol.57 (12), p.3466-3471
• Main Authors: Asadi, K, Wildeman, J, Blom, P W M, de Leeuw, Dago M
• Format: Article
• Language: English
• Subjects: Applied sciences; Blends; Circuit properties; Contact; Current density; Depolarization; Design. Technologies. Operation analysis. Testing; Diodes; Electric, optical and optoelectronic circuits; Electronic circuits; Electronics; Exact sciences and technology; ferroelectric; Ferroelectric materials; Ferroelectricity; Integrated circuits; Integrated circuits by function (including memories and processors); Nonvolatile memory; Polymer blends; resistive switch; Retention; retention time; Semiconductor device measurement; Semiconductor diodes; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Semiconductors; Switches; Switching, multiplexing, switched capacity circuits
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/TED.2010.2072958

Resistive switches have been fabricated using a phase-separated blend film of ferroelectric random copolymer poly(vinylidene fluoride-co-trifluoroethylene) with the organic semiconductor regio-irregular poly(3-hexylthiophene) (rir-P3HT). Spin-coated blend films have been contacted with symmetrical Ag top and Ag bottom electrodes, yielding switching diodes. The ferroelectric polarization modulates the injection barrier, yielding an injection-limited off-state and a space-charge-limited on -state. To study the effect of depolarization, an additional polyphenylenevinylene-type semiconductor layer with the highest occupied molecular orbital energy that is comparable to that of rir-P3HT has been inserted in the diode stack. When the ad-layer is the injecting contact, the current modulation ratio goes to unity. The origin is a decrease in the effective band bending at the contact with increasing ad-layer thickness. When the counter electrode at the blend interface is the injecting contact, the diode can be switched, but the on-state is only stable when an electric field that is larger than the coercive field is applied. Upon field removal, the ferroelectric depolarizes, and the current drops to that of an unpoled pristine diode. The depolarization is confirmed by capacitance-voltage and retention time measurements. To realize bistable diodes with excellent retention times, the thickness of the semiconducting wetting layer may not be at most 10 nm.